The nitric oxide-producing activities of Scutellaria baicalensis

Scutellaria baicalensis (SB) has antibacterial and antiviral activities. Ni tric oxide (NO) as a potent macrophage-derived effector molecule against a variety of bacteria, viruses and tumors has received increasing attention. The objective of this study was to determine the effect of SE on the produc tion of NO. Stimulation of mouse peritoneal macrophages with SE after the t reatment of recombinant interferon-gamma (rIFN-gamma) resulted in the incre ased NO production. SE had no effect on NO production by itself. When SE wa s used in combination with rIFN-gamma, there was a marked cooperative induc tion of NO production in a dose-dependent manner. The optimal effect of SE on NO production was shown 6 h after treatment with rIFN-gamma. NO producti on by SE was inhibited by N-G-monomethyl-L-arginine. The increased producti on of NO from rIFN-gamma plus SE-stimulated cells was decreased by the trea tment of protein kinase C inhibitor such as staurosporin. In addition, syne rgy between rIFN-gamma and SE was mainly dependent on SE-induced tumor necr osis factor-alpha (TNF-alpha) secretion. All the preparations of SE were en dotoxin free. These results suggest that the capacity of SE to increase NO production from rIFN-gamma-primed mouse peritoneal macrophages is the resul t of SE-induced TNF-gamma secretion. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.